As a generator mounted in an internal combustion engine, a magneto generator comprised of a rotor that produces a magnetic field by mounting a permanent magnet to a rotor yoke, and a stator having polyphase armature coils has been used. A rotating electric machine comprised of a rotor having a magnetic field and a stator having polyphase armature coils operates as a generator when the rotor is externally driven. Such a rotating electric machine operates as a motor when a drive current is passed through the armature coils while an excitation phase is switched according to a relative positional relationship between the magnetic field of the rotor and the armature coils.
For example, an inverter circuit is provided between a battery and armature coils of a rotating electric machine comprised of a rotor having a magnetic field and a stator having polyphase armature coils, and a combination of switch elements of the inverter circuit that need to be turned on at each position of the rotor in order to rotate the rotor in a predetermined direction is regarded as a switch pattern, and the inverter circuit is controlled while the switch pattern is switched according to the position of the rotor (a positional relationship between the magnetic field of the rotor and the armature coil of each phase), thereby allowing the rotating electric machine to be operated as a motor.
Thus, the rotating electric machine comprised of the rotor having the magnetic field and the stator having the armature coils may be operated as both the generator and the motor, and as disclosed in Japanese Patent Application Laid-Open Publication No. 2004-80931, it has been considered that a rotating electric machine mounted in an internal combustion engine is operated as a motor at the start of the engine to start the internal combustion engine, and after the engine is started, the rotating electric machine is operated as a motor to charge a battery by using output of the rotating electric machine. Such a rotating electric machine is referred to as a starter generator.
When the rotating electric machine comprised of the rotor having the magnetic field and the stator having the polyphase armature coils is operated as the motor, as disclosed in Japanese Patent Application Laid-Open Publication No. 2004-80931, a polarity of a magnetic pole of a rotor is detected by a magnetic sensor comprised of a Hall element to detect a position of the rotor where a switch pattern of an inverter circuit is switched. A resolver has been also known as a sensor for detecting a position where a switch pattern is switched.
As disclosed in Japanese Patent Application Laid-Open Publication No. 2004-173482, it has been proposed that when a rotating electric machine of a magnetic field rotation type is operated as a magneto generator, an AC control voltage is applied to an armature coil of a stator from voltage storage means such as a battery or a capacitor provided on a load side of the generator via an inverter circuit to control output of the generator.
In the magneto generator, the magnetic field of the rotor is produced by a permanent magnet, and thus the magnetic field cannot be controlled by a method similar to that for a generator having magnetic field winding to control an output of the generator.
Thus, in the invention disclosed in Japanese Patent Application Laid-Open Publication No. 2004-173482, the generating device is comprised so as to apply the AC control voltage having the same frequency as an induced voltage of the armature coil to the armature coil from the voltage storage means such as the battery or the capacitor provided on the load side via the inverter circuit, wherein a phase of the AC control voltage is changed to change a magnetic flux linking the armature coil and change an output characteristic of a magneto generator.
When the rotating electric machine of the magnetic field rotation type is operated as the generator, the AC control voltage having the same frequency as the induced voltage of the armature coil is applied to the armature coil to change a phase angle of the AC control voltage to a delayed side relative to a phase of a no-load induced voltage of the armature coil, thereby generally increasing an output of the generator. The phase angle of the AC control voltage is changed to an advanced side, thereby reducing the output of the generator. The phase angle of the AC control voltage relative to the phase of the no-load induced voltage of the armature coil is referred to as a “control angle”.
As described above, when the rotating electric machine of the magnetic field rotation type is operated as the generator, depending on whether the output of the generator (an output voltage or an output current) is lower or higher than a target value, the control angle is changed to the delayed side or the advanced side to allow control for matching the output of the generator with the target value. Such control that the generating device is comprised so as to apply the AC control voltage to the armature coil from the voltage storage means provided on the load side via the inverter circuit, and the phase angle of the AC control voltage is controlled to adjust the output of the generator is referred to as “drive control”, which means controlling the output of the generator while driving the generator from the load side.
In the drive control, a position of a rotor (a relative positional relationship between a magnetic field and an armature coil of each phase of a stator) needs to be detected in order to determine the phase angle of the AC control voltage. The position of the rotor can be detected by using a Hall element. In the invention disclosed in Japanese Patent Application Laid-Open Publication No. 2004-173482, however, the position of the rotor is detected by using a signal generating device that detects an edge of a reluctor to generate a pulse signal when a rotational angle position of the rotor matches a predetermined position.
For a brushless motor, as disclosed in Japanese Patent Application Laid-Open Publication No. 60-194782, a method has been known for detecting a position of a rotor from changes in reverse induced voltages of armature coils without using a sensor such as a Hall element. In the method disclosed in Japanese Patent Application Laid-Open Publication No. 60-194782, a resistor circuit comprised of three resistors star-connected is connected in parallel with three-phase armature coils star-connected, the sum of the reverse induced voltages of the three-phase armature coils is detected from a potential difference between a neutral point of the armature coils and a neutral point of the resistor circuit, and the position of the rotor is detected based on a change in the sum of the reverse induced voltages.
The Hall element has low heat resistance, and thus if the Hall element is used as a sensor for detecting the position of the rotor where a switch pattern of an inverter circuit for controlling supply of a drive current to armature coils is switched when a rotating electric machine is used in high temperature environments such as when a rotating electric machine comprised of a magnet rotor mounted to a crankshaft of an internal combustion engine and a stator having polyphase armature coils is operated as a brushless motor to start the engine, the Hall element may be damaged by heat from its surroundings.
When a resolver is used as a sensor for detecting the position of the rotor where the switch pattern of the inverter circuit is switched, the resolver itself is expensive, and a detection circuit for detecting a phase difference between an excitation voltage and an output voltage is required, which increases costs of a rotating electric machine.
As disclosed in Japanese Patent Application Laid-Open Publication No. 2004-173482, if the position of the rotor is detected by using the signal generating device that detects the edge of the reluctor to generate the pulse signal, the sensor having low heat resistance need not be used. However, the signal generating device that detects the edge of the reluctor to generate the pulse does not generate an output without rotation of the rotating electric machine, and thus the method using such a signal generating device cannot be used for detecting the position of the rotor at the start of the rotating electric machine when operated as the brushless motor.
Similarly, as disclosed in Japanese Patent Application Laid-Open Publication No. 60-194782, the method for detecting the position of the rotor from the changes in the reverse induced voltages of the armature coils can be applied only when the rotating electric machine is rotated and the armature coils generate the reverse induced voltages, and thus cannot be used as the method for detecting the position of the rotor at the start of the rotating electric machine.